1. Field of the Invention
The invention relates to a biological sterile indicator for monitoring sterility or disinfection, etc., having a carrier surface containing functional groups which are covalently bonded to one or more microorganisms through a crosslinking reagent. The indicator desirably contains a uniform and consistent microorganism population which can be utilized in evaluating various sterilizing treatments of medical devices and accessories, instruments, solutions, surfaces, clothes, and the like, to indicate the degree or success of sterilization with respect to articles that are to be reused or terminally sterilized.
2. Description of the Prior Art
Biological indicators are used to test and/or determine the effectiveness of sterilization processes. A typical biological indicator contains a calibrated population of microorganisms having a high resistance to the sterilization process under investigation. After exposure to the sterilization process, the biological indicators are incubated in a culture medium to encourage growth of any remaining viable microorganisms. Self-contained biological indicators contain the culture medium within the indicator, typically in a frangible vial. Spore strip biological indicators are combined with a separate container of culture medium after the monitored sterilization process. Subsequent microbial growth, as demonstrated by a color change or turbidity of the growth medium, is an indication that the sterilization process was ineffective.
Bacterial spores are typically favored for biological indicators due to the fact that microbial spores are accepted as being more resistant to sterilization processes than most other types of microorganisms, and thus it is assumed that a sterilization process that will kill microbial spores will also kill any other contaminating microorganism.
The choice of bacterial spores is dependent upon the sterilization mode, sterilization type, and technique to be evaluated. For example, Geobacillus stearothermophilus spores are used to monitor sterilization systems employing moist heat, peracetic acid, hydrogen peroxide, and other peroxy compounds in both the liquid and vaporous state because these indicator spores are highly resistant to oxidative chemistries. Similarly, Bacillus subtilis spores are employed to monitor ethylene oxide sterilization, and dry heat sterilization systems.
The microorganisms are generally supported on a carrier or substrate, such as a strip or disk. The substrate is formed from a material which is compatible with the sterilization process and does not contain additives which may influence the sterility assessment. Materials such as filter paper, chromatography paper, blotter paper, glass fibers, polymer plastics, ceramics, stainless steel, and metaloxide articles are often used as a substrate or carrier.
To distribute the organisms on the substrate, a suspension of microorganisms in water or alcohol is conventionally pumped to a needle which is suspended over a web of the paper or other substrate material. The paper is moved under the needle at a constant rate, causing a trail of suspension to form on the paper as it passes beneath the needle. Alternatively, the suspension is manually transferred by use of a micropipette to the substrate. The web of impregnated paper is then cut to the appropriate size for use as the indicator, typically as test strips or test disks.
As well as the necessity for a controllable quantity of the microorganism to the substrate surface, it is important that the microorganism be sufficiently immobilized on the surface of the substrate. Various types of linkages of the microorganism to the substrate surface have been proposed, including hydrophobic and electrostatic interactions, ion exchange, and van der Waal's forces. U.S. Pat. No. 4,478,946, relates to the adsorption of nonfunctional proteins to a surface and the employment of crosslinking agents to covalently attach functional proteins to adsorbed non-functional proteins. However, such immobilization techniques often provide less than desirable attachment, especially in aqueous environments. U.S. Pat. No. 5,077,210 relates to active agents such as proteins covalently immobilized on substrates carrying hydroxyl groups. A silane is bound to the substrate and coupled to a heterobifunctional crosslinker at one functional group leaving a free functional group, different than the first group, to which a protein is bound while retaining high protein functionality. The silane has a functional group which reacts with the hydroxyl group of the substrate and a thiol terminal group which reacts with a functional group of a heterobifunctional crosslinking agent which contains a succinimide group that reacts with an amino group of the active agent.